That's odd. Which video player do you use?
I just checked playing files from both Library & p2p windows, shared & non-shared using VLC - (click on link) & all launched & played happily. We generally recommend VLC here as a great alternative player. Either as a backup player or setting as default video player. It has all its codecs built-in & plays all video types you will find on the network. Also plays a wide range of audio files too.